Home TroubleshootingEngine Oil In Coolant – Do You Have A Blown Head Gasket?

Oil In Coolant – Do You Have A Blown Head Gasket?

by Kelvin Yates

So, you’ve noticed a few problems with how the car’s driving, and it’s leaving a pit in your stomach. The engine is overheating. It’s lost power and misfiring, and there might be white smoke coming from the exhaust. With a feeling of dread, you open the hood and find oil in the coolant reservoir.

Oh, dear.

All the signs are pointing towards a blown head gasket.

Although now is not the moment to panic, a reality check is also necessary. There aren’t many other possibilities in this situation – you, unfortunately, may well have a blown head gasket. Without panicking, now’s also the time to accept that the repair costs aren’t going to be insignificant.

You’ll need to get the car towed to the nearest workshop that agrees to work on it.

In this article, we’ll be considering why having oil in your coolant often represents a blown head gasket. Not exclusively… but often. I’ll also explain what you should do and how much you should expect to pay for a repair or replacement.

What Is A Head Gasket

Your car’s engine is made up of an engine block and a cylinder head, with slight variations on the names’ particulars.

In a standard engine, the cylinder head sits on top of the engine block.

The engine block contains your pistons, cylinders, con-rods, etc. Depending on the specific engine type, the cylinder head may or may not contain:

  • Camshaft (or camshafts in a DOHC),
  • Intake valves, and
  • Exhaust valves.

Most modern cars will have all three of these sets of components in the cylinder head. This fact is true of most vehicles with SOHC (Single Overhead Camshaft) or DOHC (Double Overhead Camshaft) engines.

Older engines, such as Overhead Valve, Sidevalve, and Inlet-Over-Exhaust models, have the camshaft in the block. Inlet-Over-Exhaust engines also have exhaust valves in the block. In contrast, Sidevalves have both exhaust and inlet valves housed in the block.

A gasket is something you can think of as a seal. The solid kind. It sits between two surfaces and is slightly compressible, causing the original two surfaces to be flush. You find other sorts of gaskets all over a car.

The head gasket sits in between the engine block and the cylinder head. Its primary function is to make the gaps between these two components negligible or non-existent.

Engine oil and coolant flow in channels through the block and head, keeping everything lubricated and at the optimal temperature. Because of the head gasket, oil and coolant flowing between the block and head shouldn’t leak out from their designated spaces.

Essentially, the head gasket keeps the oil, coolant, and everything in the combustion chamber exactly where it should be as it passes between the head and the block.

What Is A Blown Head Gasket

When we’re talking about a “blown” head gasket, we are referring to a head gasket that no longer does the previous job of sealing in oil, coolant, and the contents of the combustion chamber.

A head gasket can “blow” by warping, wearing down, cracking, or otherwise splintering or disintegrating.

We also talk about other components of cars “blowing” – for example, exhausts. When the exhaust is blowing, it has a hole or cracks in it somewhere it shouldn’t. Due to this, it doesn’t do its job correctly. It’s the same situation with the head gasket.

Oil In Coolant Reservoir

The head gasket contains precisely-engineered holes that allow the oil or coolant to pass through it in exactly the right position. For example, the oil or coolant travels through a channel in the block and goes straight into a perfectly lined-up channel in the head, passing through the gasket at the transition point.

When the head gasket blows, some of this oil or coolant might leak as it passes through. Because of the extremely high pressures, the oil can find its way into the coolant channels and vice versa.

From here, the contaminated coolant contained cycles all around the engine as you drive. When you stop and switch the engine off, you’re likely to notice the oil in the coolant reservoir – unless there’s a separate leak somewhere.

This is a problem that will continue to exacerbate until it gets fixed properly.

Blown Head Gasket Symptoms

Oil In Coolant

There are many little – or big – signs that can also point towards a blown head gasket.

To sum them all up, anything to do with engine oil, coolant, or engine performance could be caused by it.

Here is a non-exhaustive list of things for you to look out for…

Oil In Coolant Symptoms #1: White Smoke Coming From The Exhaust Pipe

White smoke from the tailpipes represents coolant being burnt in the combustion chamber. You might also smell a sweet, fruity aroma in the smoke. It’s leaking in and being detonated in the power stroke along with the air/fuel mixture. The coolant may well be leaking in due to a blown head gasket. For more in-depth information on that issue, click here to read an article dedicated to it.

Oil In Coolant Symptoms #2: Blue Smoke From The Tailpipe

In the same way, as white smoke represents burning coolant, blue smoke (or blue smoke from exhaust on startup) is a telltale sign of burning motor oil. It doesn’t necessarily mean you have a blown head gasket – there are lots of other things that could be the cause – but it could.

Oil In Coolant Symptoms #3: General Loss Of Engine Power

While an almost limitless amount of things could cause this, a blown head gasket would also lead to this happening. When the head gasket is no longer sealing in the cylinder’s compression, the force with which explosion drives the piston down is considerably reduced. This leads to the overall power output of the engine is inadequate, unbalanced, and inconsistent.

Oil In Coolant Symptoms #4: Coolant In The Oil

We’ll go into this in a little more detail in one of the below sections. In short, you might notice a milky-type discoloration of your engine oil. This discoloration represents the presence of coolant. Where did it come from? Probably the head gasket.

Oil In Coolant Symptoms #5: Overheating Engine

You should always keep an eye on your temperature gauge. Engines generally run at about 100 degrees C. The little temperature gauge on your dashboard shows you this. It usually takes a few minutes of driving before the temperature begins to register on the dial as the engine warms up.

However, once it’s warm, it should settle at about 100 degrees, give or take. The manufacturer will probably have installed an “optimum” marker on the dial. If the needle goes into the red, watch out – the engine is overheating.

When you have a blown head gasket, the engine overheats because coolant and oil should be keeping it cool. If they aren’t getting to where they should be going, the temperature keeps on rising.

Oil In Coolant Symptoms #6: Loss Of Oil And/or Coolant

A loss of oil and/or coolant, without apparent reason, is another possible symptom. If the head gasket has blown, oil or coolant may be leaking into the combustion chambers and then being sent out through the exhaust, causing the smoke colors we talked about before. This will, clearly, lead to a reduction in their levels.

Driving With A Blown Head Gasket

You can’t get away with ignoring this, sadly.

With cars – just like with anything – the longer you leave it, the worse it’ll get.

Your car will, almost certainly, be developing greater and greater problems related to heat control, lubrication, and/or cylinder compression levels with every moment it’s running.

The engine can reach the point whereby the components seize, meaning an engine swap is now the only option.

If you spot oil in your coolant, the sooner you get someone to look at the car, the better. In this situation, I wouldn’t recommend taking a chance on driving it. It is better to swallow the cost, put the car on the back of a truck, and take it to anyone nearby who might help. Alternatively, you could consider using a call-out mechanic.

This 10-minute video shows a head gasket is replaced. There’s no narration or music but it may interest you nevertheless.

What Else Could Be The Problem

Check out this video, examining a car with oil in the coolant. Notice what it looks like, too – a kind of soupy brown.

There are a couple of other possible reasons for having oil in your coolant. None of them are, sadly, particularly good news.

  1. An oil cooler is… well, it’s precisely what it sounds like. It’s a bit like an oil radiator – a heat exchanger. Many modern cars have them. Performance cars may have them too, and you can also get them as an aftermarket part. For this topic, we are explicitly thinking of oil-to-water coolers. After passing through the block but before the filter, the engine oil goes through this cooler. As it does so, the heat is transferred to the coolant through the walls. It’s then dissipated into the atmosphere through the coolant radiator in the usual way. If there’s a leak in the oil cooler, you could end up with oil in the coolant or vice versa. To fix this, you’ll need a new oil cooler.
  2. If you have cracks in either the engine block or cylinder head themselves, it’s terrible news. Worse than a blown head gasket, I’m afraid. Finding these cracks will probably require the complete removal and possible dissection of the engine. Although welds might be a cheap, temporary fix, you’ll need a new engine in reality.

How To Fix Coolant Mixing With Engine Oil

If you have a blown head gasket or cracks in the block or head, you will need to have some major work done.

Unless you are a trained mechanic or experienced with these things, you’ll probably need a professional – no matter which route you take.

On top of all of the calculations and figures below, you’ll also need to include the costs of draining and replacing the coolant and the oil. You may also want to consider replacing the oil filter and having a general inspection of significant components.

Blown head gaskets are, in some ways, the riskiest to work with because you need to know why it blew in the first place, as well as replace it with a new one.

1. Blown Head Gasket

Head gaskets usually blow due to excessive heat coming from the block, generally meaning that the coolant or oil is at fault. If you’ve really ragged your engine, too, it can cause a blown head gasket.

Sometimes it’s impossible to figure out, and you’ll need to take a risk and replace it, in which case it may blow again.

Replacing a head gasket requires the mechanic to remove the engine from under the hood and pull the cylinder head away from the block. They’ll then remove the blown gasket and carefully try to diagnose the original cause. As well as this, they’ll use precise spirit levels to check if the surface of the block or head needs machining to make it level again.

New head gaskets need to be put on very carefully, following precise instructions and using a calibrated torque wrench.

Once that’s done, the technician will reassemble the engine and drop it back into the car.

Head gaskets themselves don’t actually cost that much, but the labor time can be quite unfriendly to your wallet. It depends hugely on your local shop’s rates, so I’d highly recommend shopping around.

You can expect to pay at least $800 for a head gasket repair and probably something closer to $1,000. Sometimes, the figure may approach $2,000.

These sorts of numbers are why most people sell or scrap the car when their head gasket blows.

If you have the skills or the friends to do it yourself, you can expect to save oh-just-so-many dollars.

The cost of the part alone is likely to be between $75 and $200, depending on your vehicle. As you can see, that’s about a tenth of what you’ll be paying a shop.

Head Gasket Replacement Cost oil in coolant

2. Structural Issues With The Block Or Head

If there are structural issues like cracking, you don’t really have any choice other than to replace the whole engine.

Some might recommend welding the cracks, but this is unlikely to provide permanent structural integrity, and the problem will likely re-emerge not too far along the line.

Rebuilds aren’t really possible in this situation, either. When you have a problem with an engine’s internal components – the pistons, piston rings, con-rods, and so on – then, yes, an engine rebuild is a possibility. However, the issue here is with the block of metal housing all of these components. That’s what needs changing.

Complete engines for most cars will cost somewhere around $1,000 to $2,500, as an average ballpark figure (that’s before any labor costs are added on). It varies – hugely! – depending on your make, model, and specification.

If you drive around in an old, ordinary, A-to-B-style vehicle, you might even be able to find a good-quality, used engine for $500. Conversely, if you drive a brand-new, state-of-the-art, luxury machine, I wouldn’t be surprised if the costs went well into the tens of thousands.

On top of that figure, you’ll likely need to pay someone to install it unless you can do it yourself—the dreaded labor costs.

Although it very much depends on your car, your shop’s labor rates, and a whole whack-load of other variables, a complete engine replacement is likely to cost you $2,500 to $4,000 (all in).

For obvious reasons, many people choose to scrap their car and buy a new one at this point, as it makes more financial sense.

3. Oil Cooler

We’ll finish this list with the least intimidating repair job.

If you’ve managed to narrow the problem down to your oil-to-water cooler, congratulations! This issue is ten times nicer on the wallet than the other things we’ve just been looking at. That being said, it’s not exactly pocket money.

The cost of oil coolers can vary a lot depending on your vehicle and whether or not it’s a performance part. At the low end, they cost about $100 but can go up to about $500 in some cases.

On top of this, expect to pay approximately 3 or 4 hours worth of labor – likely to come somewhere around $200.

To pluck an average figure from these calculations, a replacement oil-to-water cooler should cost you about $400-$500.

What’s My Best Option

If you’ve found oil in your coolant and read through all of the above information, you’ll know that the chances are you’re in for a hefty bill in the immediate future.

The first thing you’ll need to do is to take the car to a mechanic for a professional, thorough diagnosis. It would be best to get the car towed to the shop. After discovering the root cause of the oil in your coolant, they should run you through your options.

What you do now is up to you.

Here are a few thoughts to help you through the process.

  1. How much is the car worth to you? That is, both sentimentally and financially. I’ve said it before, and I’m sure it’ll come up many times again; cars are (almost always) not financial investments. Sure, you can throw old E-Types and Porsches at me, but they’re the exception – not the rule. If you have no emotional attachment to the car, don’t be afraid to get into the numbers. Write down and calculate everything involved and every possible option, including scrapping the car or repairing it. And if you do have an emotional attachment – well, it’s not even up for debate, right? You’ll be fixing that car. One way or another.
  2. Do you use the car often? How often? Or, more accurately, how long can you do without a vehicle? Some people will do just fine for months – others, not so much.
  3. How available are the parts?
  4. Can the garage get the work done within the next few days, or is it likely to be in for a few weeks?
  5. Is the car likely to last many years after you get this work done, or is it probable you’ll have to scrap it in a couple of years anyway?

Coolant In Oil

If you notice coolant in the oil as well as the opposite way around, it’s only further evidence of a blown head gasket, oil cooler, or structural cracks.

Either way, I would recommend replacing all of the coolant and all of the oil.

Unfortunately, you’ll still need to take the car to a professional mechanic to get the engine properly inspected.

It’s best to follow the same steps and average repair figures as listed above if you find coolant in the oil rather than oil in the coolant.

Car Engine Coolant and Oil Mixing: Facts You Need to Know

  • Having engine coolant mixing with oil can cause serious damage to your car if not addressed immediately.
  • Mixing of oil and coolant generally means there is a failure in one or more of the engine’s gaskets or seals, especially the cylinder head gasket.
  • Overheating can also cause oil and coolant to mix, destroying gaskets or cracking the cylinder head or engine block.
  • Oil is designed to lubricate internal components of a car while coolant is to keep it from overheating, diluting either substance can lead to overheating and severe engine damage.
  • Cleaning the reservoir and flushing the radiator with water, and changing the oil are necessary steps to fix oil mixed with coolant in the reservoir or coolant in the oil tank.
  • Hy-per Lube Oil Supplement and Hy-per Cool Super Coolant are recommended quality products to add during oil and coolant change to prevent or reduce leaking issues and lower engine temperatures.
  • If the leak is too severe, a professional mechanic may need to look into the problem, especially if dealing with a blown head gasket, a cracked cylinder head, or a cracked engine block.
  • The cost of fixing coolant mixing with oil will depend on the severity of the problem, with temporary fixes being quite affordable.
  • The worst-case scenario is a crack in the engine block, which will require the engine’s replacement and may cost around $4,000 to $8,000.
  • Replacing the radiator or fixing the transmission should not cost more than $400 or $500, while replacing a completely destroyed head gasket could run a couple of thousand dollars.

Oil In Coolant? In Summary, You Should…

In summary?

When you see oil in your coolant, “Oh, no” is an understatement.

I feel for you, but your car’s probably had the equivalent of a heart attack. To save it, you’ll need to take drastic action, and, painfully, your bank account is likely to suffer. It’s either that, or it’s time for a new one altogether.

It’s up to you, ultimately.

The best steps are preventative ones. Check your oil and coolant regularly. Don’t overwork your engine or use cheap, not-up-to-scratch parts. Take your car to be serviced periodically and follow a trusted mechanic’s advice.

All in all, finding oil in your coolant is terrible, but with careful consideration of your needs and costs, there will be a way out and forward.

FAQs On Oil In Coolant

If you’re still curious to understand why there’s oil in coolant, then our FAQs here might help…

What Causes Coolant To Leak

There are several possible causes of why your engine is leaking coolant. The first place to check is the radiator. A rusted, damaged, or punctured radiator would see coolant leaking out of it. In relation to the radiator, there are also all the radiator hoses. Over time, the rubber in these hoses would harden and crack, causing them to leak out coolant. You may also want to check the radiator cap, as coolant could leak out of there, as well. Otherwise, there could be leaks within the expansion tank. Or, your water pump, which is needed to circulate coolant, has failed and has sprung a leak. On top of all that, another possible avenue from which coolant might leak is a blown head gasket, where coolant may mix with motor oil if that’s the case.

Do You Add Coolant To Radiator Or Reservoir

Most folks who are filling or topping up coolant for the first time often come into a similar conundrum. Do you add coolant to the reservoir, or do you fill coolant directly into the radiator? In practice, it’s generally a good idea to add coolant to the reservoir (not the radiator). This is especially so if you’re merely topping up coolant. Yet, there are a few instances where you might want to or could add coolant straight into the radiator. For example, many older or classic cars don’t have a dedicated reservoir to add coolant into. In this situation, you’re required to add coolant directly into the radiator. Alternatively, it’s also okay to add coolant straight into the radiator if the reservoir is empty (such as in the event of a coolant leak, for example).

What Does Oil In Coolant Look Like

When oil and coolant mix together, their inter-mixed concoction is immediately visible if you take a peek. In particular, take a closer look at the engine oil reservoir. Contaminated engine oil that’s been mixed with coolant will appear as a thick, milky, brownish (sometimes greenish), gravy-like liquid. Some of the residues might also be very noticeable on the oil reservoir filler cap itself. If you notice this, it’s crucial that both the coolant and oil reservoirs are both flushed. And, have the respective fluids (coolant and motor oil) changed with fresh ones. Before doing that, it’s also important that you fix the underlying issue that’s caused the two liquids to mix. Oftentimes, a blown head gasket is the cause of oil and coolant mixing together.

How To Fix Milky Oil In Engine

If you notice milky oil inside your engine, it’s crucial that you take action ASAP. This is what happens when oil and coolant mix with one another, which is quite bad for your engine should you ignore this issue and keep on driving. Milky oil won’t lubricate or cool your engine as well as it did. Thus, potentially causing extensive damage if you don’t fix it in time or keep the engine running afterward. To fix this, the entire engine needs to have all this milky oil flushed. But before you add some fresh, new oils in, you’ll have to fix the underlying issue of how it appeared in the first place. Usually, milky oil is caused by a blown head gasket. So, replacing this head gasket is a key priority that you’ll have to perform before adding some new motor oil.

What Happens If You Overfill Coolant

When you’re filling your car up with some coolant, it’s vital that you pay close attention to the coolant level. In short, you have to be wary to not under or over-fill the coolant. In the case of the latter, too much coolant is actually a very bad thing. For starters, too much coolant may substantially increase the pressure within the cooling system. Thus, potentially causing hoses, seals, and seams to rupture. Otherwise, it might even cause damage to your car’s electrics. Most cars have an overflow valve or hose which excess coolant will be released from. At the very least, you’ll see the overfilled coolant start to leak out underneath your car. Yet, some cars have these valves and hoses placed close to your car’s wiring harness, so leaks there might damage the wires.

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